This resubmission application seeks to renew support for a training program that prepares highly qualified pediatricians to assume leadership positions as investigators in Pediatric Infectious Diseases. Based in the Division of Infectious Diseases at Boston Children's Hospital, the program takes advantage of the rich academic and research resources of Harvard Medical School, Harvard School of Public Health, and affiliated teaching hospitals to bring together outstanding didactic experiences and research opportunities relevant to infectious diseases of children. Support for four positions per year is requested. Pediatricians enter the program for a minimum of three years of integrated clinical and research training that includes at least two years of supervised research under the mentorship of a member of the teaching faculty. Research training of pediatricians is fully integrated with that of PhD postdoctoral trainees in the laboratories of the teaching faculty. The 31 members of the teaching faculty are accomplished investigators and experienced mentors chosen from the Division of Infectious Diseases at Boston Children's Hospital and affiliated units at other Harvard institutions. Under the guidance of the research mentor and the Program Steering Committee, an individualized curriculum is designed for each trainee in one of three broad areas of investigation: microbial pathogenesis, host response and vaccines, or epidemiology and health outcomes. Trainees in the epidemiology and health outcomes pathway have the opportunity to earn a Master of Public Health degree from the Harvard School of Public Health as an integral part of the training program. Trainees in the other pathways also receive training in epidemiology, biostatistics, clinical trial design, and analytic methods. All trainees have seminars and tutorials in grant preparation and scientific writing that supplement the mentored research experience. An individual Scholarship Oversight Committee is appointed for each trainee to monitor progress and to provide career guidance. During the second or third year, trainees are expected to present their work at national meetings, to prepare one or more manuscripts for publication, and, in most cases, to apply for a K08, K23, or other career development award to support the transition to independence as an investigator. During the initial five years of this training grant, 11 pediatrician trainees and 4 PhD postdoctoral fellows have been supported by the grant. Of the 13 fellowship program graduates during this period, 12 have academic faculty or government research appointments. Six have received competitive individual fellowship and/or grant awards including 5 K08 or K23 awards, 2 R21, 1 R03, and a New Innovator award from NIH.